The present invention relates to a three-piece solid golf ball. More particularly, it relates to a three-piece solid golf ball, of which flight distance is improved by accomplishing high launch angle and low spin amount in initial flight performance, while maintaining soft and good shot feel, when hit at low head speed.
In golf balls commercially selling, there are solid golf balls such as two-piece golf ball, three-piece golf ball and the like, and thread wound golf balls. Recently, the two-piece golf ball and three-piece golf ball, of which flight distance can be improved while maintaining soft and good shot feel at the time of hitting as good as the conventional thread wound golf ball, generally occupy the greater part of the golf ball market. Multi-piece golf balls such as three-piece golf ball have good shot feel while maintaining excellent flight performance, because they can vary hardness distribution and design of golf balls, when compared with the two-piece golf ball.
A golf ball has many depressions called xe2x80x9cdimplesxe2x80x9d on the surface. The dimples have function to disturb airflow around the golf ball on the fly and to facilitate turbulent transition at boundary layer so as to give rise to turbulent separation, which is called xe2x80x9cdimple effectxe2x80x9d. The facilitation of turbulent transition sifts the separation point of air from the golf ball to backward and reduces a drag coefficient, to result in an increase of flight distance. In addition, the facilitation of turbulent transition increases a difference of the separation point between an upper side and a lower side of the golf ball, caused by backspin of the golf ball, and enhances lifting power applied on the golf ball. Therefore, the properties of dimples have been adjusted to a proper range in order to improve the flight performance.
The three-piece solid golf balls are obtained by inserting an intermediate layer between the core and the cover layer constituting the two-piece solid golf ball and have been described in Japanese Patent Kokai Publication Nos. 313643/1997, 305114/1998, 70408/2000, 70409/2000, 70414/2000, 254252/2000 and Japanese Patent Nos. 2570587 and 2658811. In the golf balls, it has been attempted to compromise the balance of flight performance and shot feel at the time of hitting by using thermoplastic resin, such as ionomer resin, thermoplastic elastomer (such as polyurethane-based thermoplastic elastomer) or mixtures thereof for the intermediate layer, to adjust a hardness, hardness distribution and the like of the core, intermediate layer and cover, properties of dimples and the like to proper ranges.
In Japanese Patent No. 2658811, a three-piece solid golf ball, of which an intermediate layer is placed between a center core and a cover, is described. The center core has a diameter of not less than 26 mm, a specific gravity of less than 1.4 and a JIS-C hardness of not more than 80, the intermediate layer is mainly formed from polyester-based thermoplastic elastomer and has a thickness of not less than 1 mm, a specific gravity of less than 1.2 and a JIS-C hardness of less than 80, and the cover has a thickness of 1 to 3 mm and a JIS-C hardness of not less than 85.
In Japanese Patent Kokai Publication No. 254252/2000, a golf ball having a multi-layer structure of at least three layers, of which an intermediate layer (cover inner layer) is placed between a core and a cover, is described. The core has narrow hardness distribution, and the golf ball has a hardness distribution such that the surface of the core is the softest and the hardness successively increases in order of the surface of the core, the intermediate layer (cover inner layer) and the cover (cover outer layer), and properties of dimples (a diameter of the dimple, depth of the dimple and total number of the dimples) are adjusted to proper ranges.
However, in the golf balls described above, it has been problem that when hit at low head speed, high launch angle and low spin amount are not accomplished, and flight performances is degraded, or shot feel is hard and poor. In addition, the problem has not been considered. There has been no golf ball, which is sufficient to accomplish the balance between flight performance and shot feel at the time of hitting. It has been required to provide golf balls, of which the shot feel and the flight performance are improved still more.
A main object of the present invention is to provide a three-piece solid golf ball, of which flight distance is improved by accomplishing high launch angle and low spin amount in initial flight performance, while maintaining soft and good shot feel, when hit at low head speed.
According to the present invention, the object described above has been accomplished by providing a three-piece solid golf ball, of which an intermediate layer is placed between a center and a cover, and by adjusting hardness distribution of the center; hardness distribution between each layer and the contiguous layer in the golf ball; and a ratio of the golf ball surface area occupied by the dimple to the total surface area of the golf ball and the total of a periphery length of the dimple to specified ranges, thereby providing a three-piece solid golf ball, of which flight distance is improved by accomplishing high launch angle and low spin amount in initial flight performance, while maintaining soft and good shot feel, when hit at low head speed.